The ignition of electrically heated rods of spectroscopic graphite subjected to transverse streams of oxygen or air at various velocities has been studied. Pre-ignition combustion occurs within the pores of the graphite but does not completely penetrate the rod (0·6 cm dia.); the conditions for ignition are therefore partly determined by the diffusion of oxygen into the pores. Ignition is facilitated by oxidizing the graphite prior to testing and hindered by depositing pyrolytic carbon in the pores. The conditions for ignition are discussed with reference to the theory of Frank-Kamenetskii,⁽¹⁾ extended to include the effect of pore-diffusion on the combustion kinetics. The practicability of calculating ignition temperatures from published kinetics data and physical properties is explored in some detail. It is concluded that the accuracy of the calculations is limited severely by uncertainties in the kinetics data and in knowledge of the degree of activation of the graphite (or other carbon) by the oxidant before ignition.